A Little Problem
by LynxWolFox
Summary: When doofenshmirtz's newest inator zaps Phineas, Ferb has to find a cure, and Isabella has to take care of the triangle headed inventor. But she soon learns that it won't be easy! (slight Phinbella)
1. Chapter 1

**Author's note: FINALLY I STARTED OFF WITH THIS FANFIC. It's been months (years in teenage timeline) since I got the idea, but lazyness kept on stopping me all the time DX**

**But now it's herererereeeeee! Enjoy!**

**Disclaimer: I don't own Phineas and Ferb. Dan Povenmire, Jeff Swampy Marsh and Disney own them.**

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><p>One day, at the Flynn-Fletcher residence, Isabella Garcia-Shapiro opened the gate to the backyard and saw her neighbors Phineas and Ferb, dressed up in lab coats, wearing goggles and using their portable laboratory kit. She watched as the red headed inventor poured some red liquid into a vial filled with some blue material, changing its color to purple.<p>

"Wat'cha doing?" Isabella asked in her cute voice.

"Oh, hi Isabella" Phineas greeted their visitor. "Ferb and I decided to create and elixir that can change things or people's color".

"That sounds cool! Can I help?"

"Of course!"

As Isabella got herself a pair of goggles and a lab coat on, Phineas noticed something was missing.

"Hey! Where's Perry?"

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><p>Meanwhile, at the <em>"Doofenshmirtz Evil Incorporated!" <em>, Perry was already trapped in a chair wheel. He was listening to Dr. Doofenshmirt's rambles about his horrible childhood.

"So, Perry the platypus, once I fire my brother Roger and the policemen and important people in the entire Tri-State Area with this inator right here, I will have control over the ENTIRE TRI STATE- wait a minute! I already said that phrase at the start. I don't want to sound repetitive or anything. I should really prepare my evil monologue BEFORE you come in, don't you think, Perry the platypus?"

Perry only chattered in response.

"Anyway. Where was I? Oh, right! So, once this machine takes effect on people, they will be completely defenseless against me! Even though, if you hit someone who has already been shot with my machine, another shot would make him or her back to normal. But that's the only way I personally know on how to make them back to normal, and you, Perry the platypus, will never get your hands on my ina-" Before he could continue with this rambling, Doofenshmirtz was kicked in the face by Perry the platypus.

"Aw, C'mon! Do you know how hard it was for me to modify that chair wheel to make it into a platypus sized trap!? It even cost more than the materials I used for the inator! Next time I'll use more conventional traps"

Soon, they started off with their everyday fight, stopping at the middle of the brawl to rest and have some tea and cookies.

Finally, Perry pushed Doof and made him fall over his own inator, accidentally adjusting it to its reverse mode and pressing the "go" button. Perry went over and pressed the "self destruct" bottom.

"Oh oh…" was the only thing Doof could say, as the machine started humming, throwing smoke and erupting sparks in the air. Perry ran away as fast as he could and jumped off the ceiling.

Before the machine exploded, it let out a single ray of green light, which went right into the suburbs.

Perry was getting away on his paraglide, just in time to hear the classic "Curse you, Perry the Platypuuuus!"

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><p>"So, Stacy, I was like 'Oh, no he didn't!' and he was like 'oh yes I did!'" Candace was talking with her phone inside the car.<p>

"Candace, we're getting close to the place. You should start thinking about cutting the call" Her mom advised, as she kept driving.

"Hold on, Stacy" The orange haired girl, as she cut the phone call. "But mom! Why do I have to go to this appointment? You know I brush my teeth regularly!"

"I know, dear, but the doctor said you have to start using braces" Linda said.

"WHAIT, WHAT?! BRACES? NEVER!" Candace was starting to have a heart attack with this.

"Because, if I told you, you would have never gotten inside the car" Linda answered.

"But mom! It'll make me NOT cool with my friends"

"I'm sorry Candace, but if you want to get nice teeth, you'll have to wear them for at least a year"

"But I can't wear those- Wait a minute" Candace looked oddly around her, a serious expression on her face "bust… bust… busting sense… tingling…" She started saying.

"Wait, what?" Her mother asked, confused about her daughter's attitude.

"Mom, Phineas and Ferb are doing something bustable!" Candace suddenly shouted. "They're playing with… some sort of…" She concentrated hard. She knew she could get this "of… ELIXIRS! They're making special elixirs at home! Mom! Let's go, hurry!" Candace said.

"Wait, how can you tell?" Her mom asked, a little concerned.

"Because I can feel it in the air" Candace replied "They've been doing stuff for so long that I actually got some sort of "busting detector". I can even know what they're going to do without seeing it" Candace said.

Linda looked awkwardly at her daughter before deciding to ignore her. _'A magical elixir?' _she let out a grin _'Now that's what I call imagination overload'_

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><p>Phineas, Ferb and Isabella (who didn't have the lab coats and goggles anymore) where having fun with their new elixirs, having already turned the color of different things, filling the backyard with stuff such as a purple plant, a green mockingbird with brown spots, and, weird enough, a orange and blue stripped Irving.<p>

"Yes! I'm part of the experiments of Phineas and Ferb!" He started squealing, as he looked at his new skin color.

Phineas, Ferb and Isabella looked back at him with inexpressive faces, and slowly walked away from him. They knew it best to just ignore him.

"So, the formulas have proven to be effective, don't you think?" Phineas said in his cheerful tone.

"Definitely!" Isabella exclaimed, as Ferb just gave a thumbs up. They then decided to have a little snack and started walking to the backyard entrance to the house.

Little did they know that a beam of menacing green light was advancing at full speed directly at them.

Finally, it impacted.

On Phineas.

Phineas' face became expressionless as his body started shinning bright green. He could feel a tingling sensation course thought his entire body and give him chills. Ferb and Isabella were watching in surprise and confusion at their best friend.

The red haired boy then closed his eyes and plummeted to the ground in exhaustion, as the green light engulfed him completely.

Isabella and Ferb looked at him, concerned about what just happened. But, when the light finally disappeared from the kid's system, they discovered the change Phineas has been though and they both let out a gasp out of pure shock.

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><p><strong>muahahaha. cliffhanger. i'm evil XD<strong>


	2. Chapter 2

**Note: New chapter everybody! woot woot! And this is a long one!**

**Disclaimer: I DEFINATELLY DON'T own Phineas and Ferb, or any of the characters or places. They all belong to Dan Povenmire, Jeff Swampy Marsh and Disney.**

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><p><strong>Chapter 2<strong>

Phineas couldn't feel a thing. He could only see black. It felt as if he was sleeping. And that was technically what he was doing, after all. Finally, he started gaining consciousness again. His eyes slowly opened to a blurred vision in front of him, and he could distinguish the muffled and echoing sounds of voices in front of him.

_"Wait, I think he's waking up!" _ Was the only thing he could understand as he closed his eyes once more.

He reopened his eyes once more as he heard someone call out his name. "_Phineas…. Phineas…"_ The voice became more clearly as well as his vision. Finally, he could see who it was.

Isabella was standing in front of him, with an expression of relief, yet concern marked on her face.

"Phineas! I'm so glad you're awake!" She said, excitement showing in her tone.

That's the point in which the red haired boy felt the soft texture of silk under him. He was lying on the sofa, at the living room of his house. Isabella and Ferb where both in front of him.

"Uh… my head. What happened?" Suddenly, Phineas froze as he heard his own voice. It sounded more… high pitched. More squeaky. "Wait, what happened to my voice?" He started getting worried.

"Well, it is a pretty weird story, you know, Phineas?" Said Isabella, as though she didn't want to say what happened.

Phineas got up form the sofa, to discover something that made him really frightened.

"Isabella? Ferb? Why are you suddenly so tall?" He was right. He was as tall as Isabella's neck. Phineas got more and more nervous as he started looking around.

"I need a mirror" He suddenly said, noticing his body felt weird. He decided to go upstairs and use the full body mirror in the bathroom.

"What?! No! Wait, Phineas!" He could hear Isabella scream, evidently running behind him alongside with Ferb. She sounded pretty terrified.

Finally, Phineas got inside the bathroom and looked at himself on the mirror's reflection.

What he saw made him stare in shock as his mouth opened wide.

He was tinier. A lot tinier than before. His orange-white stripped shirt and his blue shorts where now huge to him, covering up most of his body. His head was bigger in size compared to the rest of the body, especially his eyes. He noticed how big his pupils were now.

"What… happened to me…?" was the only thing he could say, as Isabella and Ferb entered the room.

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><p>Linda was in front of the Dentist's department, pulling on Candace's arm to get her out of the car.<p>

"This is really immature, Candace" The middle aged woman exclaimed, earning a dismayed cry from the girl.

"But mom, I don't want this!" Candace moaned, before her grip on the car's backseat finally loosened up, and she fell over her mom, both of them falling on the concrete floor.

"I thought you would stop being so stubborn once you grew up" the middle aged woman said as she and her daughter stood up from the floor. "You're acting like a five year old!"

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><p>"So does this mean I'm more or less five years old again?" Phineas said, still looking at his reflection in awe.<p>

"Well, apparently?" Said Isabella, still a little confused about the events taking place, and slightly resisting on letting out an "aww!" at the cuteness of her miniaturized crush.

"Ok, this is pretty weird. But I suppose it's pretty neat too!" Phineas said cheerfully, as he made a step closer to the mirror.

But that little step made him trip with his oversized shorts and fall face first to the floor

"Phineas! Are you ok?" Isabella said, a little panicked about it.

"Yes" he said as he got up "I'm ok, don't worry" they couldn't notice him sniffing and containing tears of pain.

"Ok, I think we should get you other clothes, Phineas. We don't want you to fall again. Now, do you remember any old pair of baby clothes you used to wear that you might still have around here?"

"First of all, I'm not a baby, Isabella." Phineas said sharply, obviously bothered by being called as such. Both Isabella and Ferb looked a little shocked when they heard his irritated tone. "And Second, I think mom would still have a pair of old overalls in her closet. Let's go check!"

After that, they all ran inside the parent's bedroom. Phineas sat at the end of the bed, while Ferb and Isabella checked on the closet, the latter feeling a little uncomfortable about sticking her nose in other people's properties.

While they looked for something useful, Phineas started having a weird feeling in his head. It was something he almost never felt. He didn't want to just sit there and look the two big kids look something at some old plain closet.

"I'm bored" He said out loud, crossing his arms, and putting an angry frown.

Isabella and Ferb looked up to him, surprised by his way of acting. They both noticed that, since his transformation, Phineas seemed grumpier. That was very unlike him. At lest, It was for a ten year old boy.

"Ferb, I'm starting to believe that Phineas hasn't only changed in size. "Came Isabella's whisper to Ferb, as not to let the little toddler to hear them. Ferb just nodded at the comment. "So I suppose we should take care of him now to prevent any problems. Don't you think?" Again, Ferb's response was a firm nod.

But, when Isabella and Ferb turned over to watch Phineas again, they looked up in fright, for he was no were in sight.

"Phineas? Where are you?" Isabella said as she and Ferb started advancing slowly to find him.

Suddenly, they felt something touch their backs and they both immediately shrieked in fright as they jumped and turned around.

There, rolling on the floor was Phineas, laughing his head off because of the reaction the two big kids had to his little joke.

"You should have seen your faces!" Phineas said.

Before Isabella could get him, he ran away into the corridor of the house.

She sighed and went to look for him in the corridor, calling him out loud. She decided to check on Phineas' and Ferb's room.

"Phineas, you'd better not scare me again or I'll-" She entered the room to find the toddler jumping on his own bed.

"Wooohoo! I've never noticed my bed was that fun!" He exclaimed, as he jumped higher. Finally, Isabella caught him midair with her arms.

"Got'cha!" She said.

Phineas frowned and started squirming like a worm, trying to get off Isabella's grasp.

"You're mean" Phineas pouted.

"Listen, Phineas. I'll let you go, If you promise to stay still and don't run away again. Ok?"

"Ok" He promised.

Isabella let him go and decided to continue searching in the closet, but before she had made one step, she had a weird feeling. She decided to look behind here and was not amused to discover Phineas had banished again.

Finally, Ferb came up to her.

"Found anything, Ferb"

"Not yet, but there's still places I haven't checked" The Brit answered.

Before Isabella could reply a thing, they heard a loud crash coming from downstairs. They both ran down as fast as they could and went to the kitchen.

They saw Phineas sitting on the kitchen table, looking to the floor, where a completely broken plate could be seen.

"Ups" Was the only thing Phineas could mutter.

Isabella boiled up in anger. "PHINEAS! You're not supposed to break stuff, or run away or… or…" She couldn't finish the phrase. She stopped almost immediately when she saw Phineas' face. It was changing from expressionless to really sad.

Isabella noticed almost immediately what was bound to happen next.

"No, Phineas! Don't you dare" She tried to stop him before it was too late.

His mouth started trembling.

"Please don't, Phineas. I'm so sorry for yelling at you!" Isabella was getting more desperate.

His eyes were starting to get watery.

"No! Please don't, Phineas! I'll play with you now if you want! We'll have fun!" She tried one last time.

But it was too late.

The incredibly strong sound of crying and wailing filled the area, making Isabella and Ferb grimace as they covered their ears. Isabella tried urgently to make Phineas stop. She finally picked him up and took him to the living room.

"Ferb! Please pick up the broken plate!" She screamed at top of her lungs. Ferb immediately grabbed a broom and started cleaning the mess.

Isabella sat the crying Phineas on the couch and tried to find something urgently to make him calm down.

Perry, who had come back from his mission, grimaced, wondering where did that cry come from. Before he could get away, he felt a pair of hands grab him. He looked up to see Isabella, with a desperate expression in her face, bags under her eyes and messed up hair. _'Wow, talking about a bad day.' _He though. He was immediately taken to the source of the wailing and was shocked to find his owner being a 5 year old.

"C'mon, Phineas! You like Perry, don't you?!" The black haired girl said, as she put Perry in Phineas' lap. He looked at Perry, and his crying became calmer. "That's it, Phineas. Everything's fine, there's no problem"

Finally, Phineas became completely silent and, though he still had some tears in his eyes, he grabbed Perry and hugged him like a plushy. The platypus couldn't care less. As long s his owner was happy (and that crying stopped), everything would be fine. But he still needed to help the toddler to become normal again, because he could already see that the problem had "Doofenshmirtz" written all over it.

"Okay, Phineas. Are you better now?" Isabella asked as soon as he stopped hugging Perry.

He nodded yes and pulled out a little smile.


	3. Chapter 3

**I'm back from my vacation, people! and that means more writing (I guess XD).**

**Yeah, this is a pretty short chapter compared to the others. Sorry for that ^v^'**

**Disclaimer: OF COURSE I do not own the characters in the story, as well as the settings and stuff. They all belong to their awesome creators, Swampy Marsh and Dan Povenmire.**

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><p>Ferb walked towards the girl and the little boy, who had the platypus still on his lap.<p>

"I think we should start trying to make an antidote" he said, a little annoyed by his wailing. Isabella agreed completely with him.

So they went to the garage and Ferb opened his portable laboratory kit, while Isabella kept and eye on Phineas, who was sitting in a chair. Perry decided to go to Doof's once more to fix things up.

"How long do you think it will take, Ferb?

"I'm not sure. I'm not that good at inventing without Phineas, so it might take a while"

"I'm hungry" they both looked up to Phineas, whose stomach was rumbling.

"Don't worry, Phin. I'll get you something to eat" Isabella responded, as she picked up Phineas again and took him into the house and into the dinning room, where she sat Phineas on a chair. But, when she went to the kitchen, she though about something obvious.

"There's no baby food in here, right?" She asked to Phineas, who got Irritated again.

"I am NOT a baby!" He repeated "and no, there is no baby foo- I mean, food in the house".

"Ok, then I'll suppose I have to go to the supermarket to buy some. So, Phineas, stay in the garage with Ferb while I go buy your food".

"But I want to go with you! It's not fair!" Said the kid, as he got up from his chair and walked in from of the girl

"No, Phineas. You must stay here..." Suddenly, Isabella saw the look on his face. Phineas was making the puppy eyes trick to her.

"No, Phineas, stop it! I'm not falling for that" Isabella said, trying to cover her eyes away from the cuteness.

Phineas' eyes became almost as huge as dinner plates, as he tried to pull out his cutest face ever.

"No! Please stop! It's not going to work!" Finally, Isabella gave in and sighed "ok, ok. You can come with me".

Phineas jumped with happiness.

"But, first, we have to find you some clothes" Phineas groaned in annoyance at Isabella "You can't go outside using clothes double your own height."

Isabella and Phineas went upstairs and she continued searching in the closet, until, at last, she finally found a little white t-shirt, a pair of overalls, white socks and black shoes.

"Here, Phineas" She said to the toddler "now, go to the bathroom and get changed"

"Aww! Do I have to?"

"Yes Phineas. If you want to eat, you'll have to change your clothes".

So, Phineas got inside the bathroom and, a few minutes later, he was already dressed up in his old clothes.

As they were about to open the door and go outside, Isabella warned the kid.

"Phineas, you have to stick to me at all times, alright?"

"Alright!" Answered innocently the 5 year old.

As soon as she opened the door, Phineas pulled out a mischievous grin and decided to run away. But he soon found out he couldn't. The big girl was grabbing his hand and not letting it go.

"Did you really think I would fall for that twice, Phineas?" Was Isabella's rhetorical question, as a victorious smile appeared on her face.

Phineas struggled and tried to free his hand, but to no avail. He then groaned at Isabella.

"You're a big bad meanie" he said.

"Yeah, once this is over, you'll retract your words" Isabella simply answered.

So, they started walking to the supermarket.

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><p>Candace was at the dentist, getting her braces put on. When her mom got in to see how it was going, the teenager seemed relaxed. REALLY relaxed.<p>

"Uh, Mr. Karney, has Candace been that calm the whole time?" Linda asked, a little concerned about the fact that she wasn't desperate about getting brackets and busting her brothers.

"Well, not really" The dentist said "Actually, when she got in, she was incredibly nervous."

*flashback: some minutes ago*

"CANDACE! Please stay CALM AND LET ME DO MY WORK!" The medic shrieked, as he tried to force Candace into the chair.

"NEVER! YOU'LL NEVER PUT BRACES ON ME ALIVE!" The angry teenage girl shouted, lifting the dental drill on her hand as a defense weapon.

"NURSE! BRING TWO AND A QUARTER CENTILITRES OF SEDATIVE! NOW!" Karney shouted.

*End of Flashback*

Linda looked, a little shocked, at her daughter. She did seem to have been tranquilized. Still, the mother decided to keep quiet and let the dentist do his work.

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><p><strong>Yeah. Short chapter XD<strong>


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